Arc-controlling auxiliary contact assembly for electric switches



A rl 5, 1966 c. ROSS ARC-CONTROLLING AUXILIARY CONTACT ASSEMBLY m H& Nel w 6 I Rt TC CO ma E e mm F u 91:\I 1 K INVENTOR. HUGH C. ROSS UnitedStates Parent O 3,244,843 ARC-CONTROLLING AUXILIARY CONTACT ASSEMBLY FORELECTRIC SWITCHES Hugh C. Ross, Saratoga, Calf., assignor to JenningsRadio Manufacturing Corporation, San Jose, Calif., a

corporation of Delawa'e Filed Oct. 16, 1963, Ser. No. 316,773 9 Claims.(Cl. 200-144) The invention relates to vacuum switches; and moreparticularly to the electrodes or contacts thereof which make and breakthe circuit through the switch.

In vacuum switches of high current carrying Capacity, for the purpose ofreducing contact pitting and erosion, it is desirable that localizedconcentration of a high current arc between the contact surfaces beavoided by causing the are to move about over the surface of thecontact.

One of the objects of the present invention is to provide a vacuumswitch contact structure having low contact resistance when the switchcontacts are closed, while permitting rapid breaking of the circuit witha minimum of arcing and attendant vaporization, thus extending the lifeof the contact surfaces.

Another object of the invention is the provision of a novelvacuum switchcontact structure that cooperatively associates a low resistance, highcurrent-carrying contact and an auxiliary breaking contact of highmeltng point to form a contact assembly of high efiiciency, lowtemperature operation, resulting in an increase of the working life ofthe switch many times what is normally to be expected of ordinary orsingle-c-ontact switches.

Still another object of the invention is the provision of a switchcontact assembly which permits rapid making and breaking action; and atthe same time prevents reboun ding or bouncing of the engaged contactelements such as would cause excessive arcing or welding together of theengaged contacts.

v A still further object of the invention is the provison of a dualcontact assembly for an electric switch in which parallel conductivepaths are provided through the contact area of the switch, and in whichsingle actuator means are provided for controlling the making andbreaking of a circuit through each of the parallel paths.

A still further object of the invention is the provision of a contactassembly in which conduction of electric current through the switch whenthe switch contacts are closed is channeled through parallel paths, eachof said paths being adapted to make and break at different times.

Other objects and advantages will `be brought out in the followingdescription of the invention. The invention is not limited to theshowing made in the description and drawings, since variant forms of theinvention may be adopted within the scope of the appended claims.

Refen'ing to the drawings:

FIG. l is a vertical sectional view with some of the interior partsshown in elevation and illustrating the dual contact assembly embodiedin a single-ended switch.

FIG. 2 is a fragmentary view of the contacts at the instant of closingthe auxiliary circuit through the annular or ring contacts andimmediately before the closing of the main circuit through the studcontacts. It also may 'be considered to illustrate the positions of thecontacts at the instant when the stud contacts have been drawn apart tobreak the main circuit, leaving the ring or auxiliary contacts engagedand about to be drawn apart t-o break the auxiliary circuit.

FIG. 3 is a fragmentary view illustrating both stud and auxiliarycontacts closed to provide parallel current paths through the dualcontact assembly to permit a maximum flow of current through the switch.i

In broadly descriptive terms the invention provides 3,244,843 PatentedApr. 5, 1966 a pair of stud contact assemblies each of which includes ahigh current-carrying stud contact for conducting most of the currentwhen the switch is closed; and an annular auxiliary contact assemblyconstituting a making-breaking element of low vapor pressure materialfor initiating the closing and opening cycles. This use of dual contactassemblies achieves the advantage of low contact -resistance and at thesame time reduces arcing and vaporization of contact material. Studcontacts which may be of Copper, carry major currents for either A.C. orD.C. They present low contact resistance and hence are able to carryhigh currents without over-heating. The annular auxiliary contacts onthe other hand close before the stud contacts to make" the circuit andbreak last to interrupt the main circuit, so that 'there is little or nodestructive arcing across the relatively high vapor pressure studcontacts in the main circuit, and so that any arc that forms between theannular contacts is rapidly spun about the contact 'by the interactionof the magnetic field generated 'by current flowing through the coil-lkeconductors connected to the annular auxiliary contacts and the magneticfield generated about the current arc itself.

In more specific detail, the 'switch comprises a vacuumized envelopeincluding a generally cylindrical dielectric shell 2, Conveniently ofceramics, hermetically closed at opposite ends by metallic end orterminal plates 3 and 4 on each of which a contact assembly is mounted.

Each terminal plate is hermetically united to the associated end of thedielectric shell by a fleXible metallic seal ring 5 as shown. In apractical structure, the end plates 3 and 4 are Conveniently fabricatedfrom heavy Copper, while the dielectric portion of the envelope isfabricated from an alumina-type ceramic material. Inasmuch as thetherrnal coefficients 'of expansion and contraction of these twomaterials vary widely, it is desirable that some means be utilized whichprovides a compensating factor for such expansion and contractionbetween the two materials while providing the requisite rigi-dity. Ithas been found that the structure shown is adequate for this purpose.

Rigidly mounted on end plate 3 is a centrally disposed axially extendingstud contact member 6, having a portion 7 extending out of the envelopeand useful as a means of connecting the switch into a circuit. The innerfree end of the stud member provides an inner contact portion 8 ofreduced diameter as shown, and on which a contact button 9 is brazed. Inthe construction shown the stud contact member 6 is Convenientlyfabricatcd from large diameter copper bar stock, while the contactbutton 9 may Conveniently be fabricated from a more ref ractory mate-.rial such as tungsten. The diameter of the contact button is preferablysome'w hat larger in diameter than the redu'ced diameter portion 8 of-the conductive contact member 6 in order to force a current loop toform during the passage of current through the switch.

Sldably disposed on the end plate 4 is a second stud contact member 12,having a portion 13 extending out of the envelope in opposition to theportion 7 of the opposed stud contact, and having an inner end contactportion 14 as shown of so mewhat smaller diameter than the remainingportion 12 of the stud contact and also smaller in diameter than a -flatplate-'like contact button 15 brazed thereon. The sliclable unionbetween the conductive member 12 and end plate 4 is hermetically sealedby interposing a suitable expansonable metallc bellow 16 between thestern 12 and the end plate 4. These unions may be made in any suitablernanner as by brazng at the closed end 17 of the bellows and 'heliarcwelding at the open end 18 of the bellows where it is united to the endplate 4.

As thus shown, movement of the member 12 aXially with respect to member6 will result in the contact surfaces of contact members 9 and 15 beingbrought into or 3 Q out of engagement, depending on the direction ofnovement of the member 12. It has been found that with high power vacuumswitches so const ructed, when the contact surfaces 9 and are pulledapart, an arc tends to strike between :the contact surfaces, such arcoften eroding and pitting the contact surfaces .and causing vapcrizedcontact metal to be deposited on surrounding structure, including thedielect-ric wall between the end plates 3 and 4. To preventaccumulations of such vaporized material on the diele'ctric member `fromforming a continuous condu'ctive path between the end plates, elaborateshieldlng structures forming no part of this invention have been devisedto intercept and condense vaporized contact material.

It has been found that the liberation and deposition of such vaporizedcontact material can be lessened materially and substantially eliminatedin its harmful efiect by providing auxiliary contacts in the contactassembly to carry the high momentary current when the main o-r studcontacts 9-15 are broken. As shown best in FIG. 1, the auXiliary contactassembly comprises a pair of annular plate-lke Contacts 21 and 22,as-sociated respectively with contacts 9 and 15. As clearly shown inFIG. 1, the oppositely d isposed annular auxiliary contact plates areprovided, respectively, with annular contact zones 23 and 24, each ofthe contact zones being radially spaced between the inner and outerpe-ripheries of the respective contact plate. With respect to each ofthe annular auxiliary contacts, the contact zone is defined by conicallytapered surfaces adjacent the inner and outer perip her ies of thecontact plate as shown.

To mount the ann-ular auxiliary contact plates 21 and 22 on theassociated contact members 9 and 15 so as to provide a parallel paththrough the contact assemblies, the annular contact plates 21 and 22 areresiliently supported coaXially about the -associated contacts 9 and 15,respectively, by heavy conductors 26 and 27, each spital-ly coiled aboutthe associated conductive contact members 6 or 12 respectively. The endof the coil conductor remote from the associated ann ular contact isrigid ly Secured in a mechanically strong and ele'ctrically condu ctivemanner to the conductive member 6 at a point remote from the contact 9.The other end of the coil conductor is rigid'ly welded to an annularinsert 28 which is in turn brazed to the surface of the contact 21 opposite the contact zone 23 as .shown. The insert 28 is provided with aradially extending fiange portion 29 upon which is suitably Secured adielectric member 31 having a cylindrically extending fiange 32interposed between 'the fiange 29 and the associated reducedcross-sectional portion 8 of the member 6. The dielectric member 31 rnaybe in the nature of a bushing slidably disposed on the reduced diameterportion 8 of the contact member 6 and may be Secured to the flange 29 ofinsert 28 in 'any suitable manner such as by a split spring ring (notshown) or by brazing. The annular auxiliary contact-plate 22 issimilarly supported on the contact member 1:2, and like numbers havebeen utilized to designate like parts.

Referring to FIG. 1, it will be ap parent from the relationship ofcontact zones 23 and 24 with respect to the associated contact surfaces9 and 15 of the stud Contacts that when the switch is in open positionas shown in this figure, irtward movement of the contact member 12 toclose the contacts will result in inwa rd movement of the contact 22toward the contact 2:1. The parts are proportioned so that such movementwill bring the contact zones 23 and 24 of the annular contacts into a-butting relationshp before the conta'cts 9 and 15 abut. Therefore, uponclosng of the switch into the position illustrated in FIG. 2, thecircuit wil l first be made through the annular auxiliary icontacts 21and 22. Continued movement of the contact member 12 in a closingdirection Will compress the coil conductor members 26 and 27, thusplacing the Contacts 21 and 22 under a resilient contact pressure, and,simultaneously, will tend to bring contacts 9 and 15 into abutting re-lationship. As soon as this has occurred, it will be obvous that aparallel path is provided through the contact assembly to help carry thecurrent load. Obviously, because of the relatively greatercrosssecti-onal area of the stud contacts 9 and 15, a major portion ofthe current will be carried through this set of contacts. It will ofcourse be obvious that the resilient monnting of the initially made`contacts `21 and 22 tends to prevent bounce or chatter between theseannular contacts, so as to prevent arcing or sputtering of contact metaltherefrom. At the same time, inasmuch as there is a parallel path tocarry the load, any bounce or chatter which occurs between the main orstud Contacts 9 and 15 does not result in arcing between these contacts.

Upon opening movement of the movable conducto' member 12 from theposition illustrated in FIG. 3 for example, it will be clear that thestud contacts 9 and 15 part immediately, thus breaking one of theparallel paths through the complex contact assem'bly, and shifting ontothe other parallel path, namely through the coil conductors 26 and 27and auxiliary Contacts 21 and 22, the mornentary load of the fullcurrent being carried by the switch. This shifting of the current loadthrough the auxiliary contacts prevents strikirg of an arc 'betweencontacts 9 and 15, and insures an inlimited lift expectancy for theseContacts. As movement in an opening direction continues, and the annularauxiliary contacts 21 and 22 part, an arc will be struck between thespaced contacts 21 and 22, but because of the novel mounting for theseContacts, the arc will be caused to spin in a circular path over thecontact zones 23 and 24, thus minimizng the vaporization of contactmetal which would occur if the arc were permitted to stand in one spot.Spinning of the arc is accomplished by the interaction of the magneticfield which is generated by the coil conductors 26 and 27, and themagnetic field which is naturally `formed about the arc.

From the above, it is clear that one of the important functions of theelectrically conductive heavy coil springs 26 and 27, and annularauxliary contacts 21 and 22 to carry a major portion of the mechanicaland electrical burden mposed by the making and breaking sequences of theswitch, while the stud Contacts 9 and 14, carry the major electricalburden only when both sets of Contacts are closed.

Another important function of the annular auxilary contact assembly isto provide a means of spinning the arc over a relatively large surfacein order to minimize vaporization of contact metal. In this respect iti-s irnportant to note that the coil conductors 26 and 27 are wound inthe same direction with respect to the axis of the switch, so that bothof the coils 26 and 27 cooperate to generate a single magnetic field. Itis clear of course that if the coil conductors 26 and 27 are wound inopposite directions, each of the coil conductors will generate its ownindependent magnetic field, and the polarity of these fields will be inopposition to each other. The eftect of opposed fields is to cancel outthe fields and prevent interaction of a single magnetic field generatedby the coil conductors with the magnetic field generated by the arc. Theetfect is manifest'ed by the tendency to drive the arc toward the innerperiphery of the annular contacts or at best keep it spinning in acircle having a fixed radius. It has been noted also that when the coilsare wound in opposite directions the diameter of the arc itself isrestricted. By comparson, when the coils are wound in the same directionas illustrated in FIGURE 1, the arc is forced toward the outer peripheryof the annular contact, thus increasing the length of the path overwhich the arc moves, and the diameter of the arc is su-bstantiallygreater, thus permitting the passage of more current. Additionally,tests have revealed that when the coils are wound in the same directionthe arc does not follow a i fixed circular path but tends to wanderov-er the faces of the annular Contacts, thus minimizing the generationof heat and the Vaporization of contact metal.

I claim:

1. In a vacuum electric switch including an envelope having a dielectricportion closed at opposite ends by metallic end plates and coaxiallydisposed stud contacts supported on opposite end plates, one of whichstud contacts is movable axially with respect to the other to make orbreak a circuit theretbetween, the improvement comprising -a pair ofauxiliary contacts coaxially dispo-sed about the stud contacts, eachsaid auxiliary contact having a contact surface lying in a planesubstantially perpendicular to the aXis of said stud contacts to permitnon-sliding abutment of said auxiliary contact surfaces, and meansmounting each of the auxiliary contacts for movement relative to theassociated stud contact upon actuation of the switch.

2. The combination according to claim 1, in which the auxiliary contacts.are proportioned to cngage before the stud contacts upon closing of theswitch to make a circuit therethrough and to disengage after such studcontacts upon opening of the switch to break the circuit through theswitch.

3. The combination according to claim 1, wheren each of the auxiliarycontacts oornprises an annular plate having an annular contact zoneradially spaced between the inner and outer peripheries thereof with thesurface of the plate immediately adjacent the contact zone tapered awayfrom the contact zone toward the inner and outer peripheries,respectively.

4. The combination according to claim 1, in which means are providedresiliently mounting each auxiliary contact respectively, on anassociated stud contact.

5. The combination according to claim 4, in which a dielectric hearingis interposed between each of the auxiliary annular contacts and theassociated stud contact.

6. The combination according to claim 4, in which said resilient meansfor mounting said auxiliary contacts comprises an axially aligned coilspring wound about the associated stud contact.

7. The combination according to claim 5, in which the end of each studcontact adjacent its contact surface is reduced in diameter to less thanthe diameter of the contact surface thereof and the dielectric hearingis slidably disposed on the reduced diameter portion of the stud contactto guide the associated auxiliary annular contact.

8. In a vacuum electric switch, -a contact assembly comprising a pair ofaxially disposed stud contacts, a pair of auxiliary annular contactssurrounding said stud contacts, and resilient means connecting saidauxiliary annular contacts to said stud contacts whercby upon actuationof the switch to make a circuit through the switch said auxiliarycontacts make contact before said stud contacts to establish a parallelconductive path through the switch and upon actuation of the switch tobreak the circuit therethrough the stud contacts break contact beforethe auxiliary contacts so that the annular auxiliary contacts alonecarry the momentary surge of current through the switch upon separationof said stud contacts.

9. The combination according to claim 6, in which the turns of the coilspring are wound in the same direction.

References Cited bythe Examiner UNITED STATES PATENTS 2,l80,66l 11/1939Baruch 200-144 3,014,l07 12/1961 Cobine et al 200--144 3,017,480 1/1962Klaassen 200-146 FOREIGN PATENTS '3,101 1/ 1954 Great Britain. 787,84612/ 1957 Great Britain.

ROBERT S. MACON, Acting Pr'mary Exam'ner.

KATHLEEN H. CLAFFY, Examner.

8. IN A VACUUM ELECTRIC SWITCH, A CONTACT ASSEMBLY COMPRISING A PAIR OFAXIALLY DISPOSED STUD CONTACTS, A PAIR OF AUXILIARY ANNULAR CONTACTSSURROUNDING SAID STUD CONTACTS, AND RESILIENT MEANS CONNECTING SAIDAUXILIARY ANNULAR CONTACTS TO SAID STUD CONTACTS WHEREBY UPON ACTUATIONOF THE SWITCH TO MAKE A CIRCUIT THROUGH THE SWITCH SAID AUXILIARYCONTACTS MAKE CONTACT BEFORE SAID STUD CONTACTS TO ESTABLISH A PARALLELCONDUCTIVE PATH THROUGH THE SWITCH AND UPON ACTUATION OF THE SWITCH TOBREAK THE CIRCUIT THERETHROUGH THE STUD CONTACTS BREAK CONTACT BEFORETHE AUXILIARY CONTACTS SO THAT THE ANNULAR AUXILIARY CONTACTS ALONECARRY THE MOMENTARY SURGE OF CURRENT THROUGH THE SWITCH UPON SEPARATIONOF SAID STUD CONTACTS.